1. Field of the Invention
The present invention relates generally to optical devices, and more particularly to optical wavelength division multiplexers and demultiplexers.
2. Discussion of the Background
Optical waveguide technology provides an enormous improvement in bandwidth compared to copper wire. It is thus poised to revolutionize communication in several fields including, telephone, television, and the Internet. Optical waveguides are increasingly used to transmit information in which high density and high speed are required. With the growth of the Internet, demands for reasonably priced optical communication solutions continue to increase.
Optical wavelength division multiplexers and demultiplexers are important elements in optical technology. An optical wavelength division multiplexer receives two or more individual wavelengths (also referred to as colors or frequencies) and combines them into one signal on a single waveguide. An optical wavelength division demultiplexer receives an optical signal with two or more wavelengths from a single waveguide and separates the optical signal into its component frequencies. Optical multiplexers and demultiplexers are crucial to take advantage of the enormous bandwidth of optical waveguides.
Technology presently exists to provide optical waveguide communications from end user to end user through a high volume network. This technique is commonly referred to as Dense Wavelength transmission and requires that anywhere from 16 to 80 different frequencies be packed into a single transmission. The frequency separation of these numerous signals is very close, about 50 GHz-200 Ghz. At the end of each transmission, a Dense Wave Division Multiplexer/Demultiplexer (DWDM) combines and separates the various frequencies. But existing DWDM are difficult to manufacture due to the difficulty in differentiating closely spaced frequencies. As such, the costs are very high. Moreover, existing DWDM are costly to operate due to their relatively high temperature sensitivity. A temperature-controlled environment is often needed to ensure their proper operation.
While these costs may be acceptable for long transmissions carrying heavy data traffic, they are unacceptably high for many short transmissions carrying low data traffic. Such low data traffic transmissions are especially common in the so-called xe2x80x9clast milexe2x80x9d of transmission (i.e., the distribution to individual locations) or for local networks. There the costs and other problems associated with DWDMs often prohibit their use. Accordingly, new devices and methods of their manufacture are desirable.
The present invention is directed toward coarse wavelength data transmission. In particular, it provides a coarse wavelength division multiplexer/demultiplexer for combining and splitting different frequencies that are not as tightly separated as commonly known dense wavelength systems. Because the tolerances of the system are not as stringent, the costs of manufacture and use as well as reliability are improved over the existing art.
Instead of the expensive band-pass filters used in the past, the present invention includes long-pass or short-pass filters to reflect wavelengths on one side of a specified frequency of the filter and to pass wavelengths on the other side of the specified frequency. Thus, a first I/O waveguide carrying an optical signal with a plurality of wavelengths is optically coupled to a second I/O waveguide through a filter. The first I/O waveguide is also optically coupled to a third I/O waveguide through filter. The filter may be a long-pass or a short-pass filter such that a first optical wavelength is reflected between the first I/O waveguide and the second I/O waveguide and a second wavelength is passed between the first I/O waveguide and the third I/O waveguide.
In an embodiment of the present invention, a dual capillary GRIN lens is optically coupled between the first I/O waveguide and the filter. The filter reflects the first wavelength between its first capillary (waveguide) and its second capillary and passes the second wavelength.
In another embodiment, the dual capillary GRIN lens is housed in a collimator assembly with the filter located between the dual capillary GRIN lens and a single capillary GRIN lens. A first collimator assembly has one of the capillaries of the dual capillary GRIN lens coupled to a first I/O waveguide and the other capillary coupled to a second similar collimator assembly. The capillary of the single capillary GRIN lens is coupled to one of the dual capillaries of a third collimator assembly. The remaining capillaries of the first, second, and third collimator assemblies are optically coupled to four additional I/O waveguides such that each is optically coupled through the collimator assemblies to the first I/O waveguide. The number of I/O waveguides and the number of collimator assemblies may be expanded or contracted to make a multiplexer or demultiplexer having a desired number of ports.
In yet another embodiment of the present invention, long or short-pass filters are optically coupled together along the optical axis of an I/O waveguide with a plurality of wavelengths. The specified wavelength of each filter changes monotonically such that each filter splits off a different wavelength and reflects that wavelength to a different waveguide. The other wavelengths pass to the next filter until all but one have been split off. The remaining wavelength passes to its own waveguide. Thus, light is reflected between the various individual waveguides and the I/O waveguide having the plurality of wavelengths. In another embodiment, the long-pass and short-pass filters are curved to focus the light as it is reflected.
A further understanding of the nature and advantages of the present invention may be realized by reference to the latter portions of the specification and attached drawings.